It is known that the treatment of seeds leads generally to an increase in the relative moisture level of the seeds. However, seeds are very sensitive to moisture which activates their germination. The tolerance of grain to water varies according to the geographical origin of production and the species of seeds. Therefore since treatment with a phytoprotection product is, for example, carried out in October for February-March sowings, it must not bring about more than 1 to 2% moisture on average in order to avoid any premature start to germination.
Drying of the seeds after treatment may be employed, but this can alter the germinating ability.
Treatment by finely sprayed suspensions in order to form a "mist" does not give satisfactory results because the cloud of droplets has a tendency to move in a body and is deposited on the seeds in a too heterogeneous fashion.
With the development of genetically improved seeds such as hybrid wheats, which are thus more expensive, sowing methods are more and more of the seed-by-seed type and no longer by the hand-sowing method (this classical technique requires, for conventional wheat, 150 to 200 kg/hectare).
It is thus important that all the seeds present in sowing receive the same quantity of treatment product. The homogeneity of the treatment also affects each grain which must be treated in a uniform manner; however, by the conventional processes, certain areas such as the seed furrow are more difficult to reach and escape treatment. The untreated pace constitutes a favoured access route for parasites.
Finally, for economic reasons and to protect the environment, one of the aims sought in the improvement of these treatments is a reduction in the quantity of active ingredient used by improving the efficiency.